Alcohol impairs driving ability more than marijuana, according to a new federally funded study.

CNN reports that the new study — funded by the National Institute on Drug Abuse, the Office on National Drug Control Policy, and federal safety regulator, the National Highway Traffic Safety Administration — found drivers under the influence of pot are more careful than drunk drivers.

The researchers said alcohol "significantly increased lane departures/minimum and maximum lateral acceleration; these measures were not sensitive to cannabis." They added that drivers under the influence of pot "may attempt to drive more cautiously to compensate for impairing effects, whereas alcohol-influenced drivers often underestimate their impairment and take more risk."

The study compared the effects of alcohol and marijuana on 19 individuals who participating in a 45-minute driving-simulator session.

Although marijuana had a less dramatic effect than alcohol on drivers the study found it still impairs "one measure of driving performance" — it reduced the drivers' peripheral vision giving them tunnel vision.

Twenty-three states and the District of Columbia have approved medical marijuana; four states and Washington, D.C., legalized recreational use for adults.

Law enforcement officials are grappling with how to establish a legal limit for stoned drivers, just as there is a .08 limit for alcohol.